--- main/rtp_engine.c	(Asterisk 11.20.0)
+++ main/rtp_engine.c	(working copy)
@@ -560,6 +560,7 @@
 	type->asterisk_format = static_RTP_PT[payload].asterisk_format;
 	type->rtp_code = static_RTP_PT[payload].rtp_code;
 	ast_format_copy(&type->format, &static_RTP_PT[payload].format);
+	ast_format_sdp_parse(&type->format, "");
 
 	ast_debug(1, "Setting payload %d based on m type on %p\n", payload, codecs);